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mode shape displacements are not abs values. They are relative values compared to max value of 1.0. The max displacement is always 1.0 and then the others are compared to this e.g. 0.5 etc. You multiply this modal amplitude values. Solve one mode shape by hand of a 2 storey frame you will get it. Anyway for separation, see it on response spectrum case or combination. For more detail you can combine modes as described in CSi ETABS Wikki help pages online. The topic is about accidental amplification of torsion in response spectrum cases. Look for that.